The ALLWISE colour–colour diagram (equivalent to Figs. 1 and 2 of Massaro et al. 2011b) with superposed HSP blazars from the Sedentary survey (blue points) and from BZCAT (red points). The Sedentary WISE Colour Domain (SWCD) is delimited by the dashed lines. For both Sedentary and BZCAT sources, as well for the sources in the SWCD, we only consider objects that meet the requirement W_{3 S/N} ≥ 2.0.